Conventionally, there has been known a technique of improving the access performance to storage devices by using cache memories that can be accessed at higher speed than the storage devices. Moreover, an operation, what is called a write back, has been also known in which when a write request to a storage device is received, data is written in a cache memory without being written in the storage device, and the updated data on the cache memory is written in the storage device in a spare time such as an idle time of processing by a central processing unit (CPU). Moreover, a technique, what is called cache replacement policies, has been also known in which when a cache memory is full and unable to additionally store new data, data that is most unlikely to be used afterward is predicted, the predicted data is discarded, and the new data is added instead.
As known related prior art, there is a technique of adjusting a heat metric threshold in accordance with caching efficiency of a present state of a secondary data storage cache; and rejecting candidate data provided to the secondary data storage cache whose heat metric is less than the heat metric threshold, for example. Moreover, there is another technique in which multiple blocks consecutive on a disk are set as one group, and when a group including a block that is updated only on a cache memory is present, the multiple consecutive blocks in the group are written back onto the disk by one access.
As examples of the related prior art, known are Japanese National Publication of International Patent Application No. 2014-535106 and Japanese Laid-open Patent Publication No. 05-303528.